Powder metallurgical processing of high-manganese steels into parts

ABSTRACT

Although high-manganese steels may have desirable mechanical strength and corrosion resistance, machining and casting can be difficult. Alternatively, high-manganese steel parts may be fabricated to near-net shape parts using powder metallurgical processing, such as hot pressing and powder injection molding, thereby significantly minimizing or eliminating the need for further machining of fabricated parts. Hot pressing processes may comprise: loading a container with a plurality of particulates comprising a high-manganese steel; establishing a reduced pressure state in the container after loading the container with the plurality of particulates, and sealing the container to maintain the reduced pressure state therein and to afford a sealed container; placing the sealed container in a pressure vessel; heating the pressure vessel at a predetermined temperature while applying a predetermined pressure isostatically to an exterior surface of the sealed container with a pressurizing gas to consolidate the plurality of particulates into a densified part having a near-net shape; and removing the sealed container to expose a surface of the densified part.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application 62/866,672 filed Jun. 26, 2019 entitled POWDER METALLURGICAL PROCESSING OF HIGH-MANGANESE STEELS INTO PARTS, the entirety of which is incorporated by reference herein.

FIELD

The present disclosure relates to powder metallurgical processing of high-manganese steels into parts having a desired near-net shape.

BACKGROUND

High-manganese steels exhibiting excellent mechanical properties in combination with good erosion and corrosion resistance have been developed for applications in various industries. As used herein, the term “high-manganese steel” refers to an alloy composition comprising at least iron, carbon and manganese, with iron being the predominant component and at least about 9 wt. % manganese being present. Additional alloying elements may be optionally present in high-manganese steels to tailor further the mechanical and/or chemical properties featured by the alloy composition.

While high-manganese steels may exhibit a desirable combination of mechanical properties and corrosion and erosion resistance, such steels tend to have relatively poor formability and are difficult to machine, each as compared to typical standard carbon steel grades. Work hardening may be particularly responsible for the difficulty in machining Difficulty in machining high-manganese steels may limit the range of parts having various shapes that may be fabricated effectively therefrom. Likewise, casting techniques for high-manganese steels may result in components (parts) having low integrity with an inconsistent or undesired microstructure. As such, the range of shapes for parts that may be fabricated from high-manganese steels remains fairly limited at present.

Currently, high-manganese steels may be readily fabricated into pipeline sections. Despite having good erosion resistance, pipeline sections comprising a high-manganese steel may still be subject to internal erosion when passing particulate-laden fluids there through, such as may occur in oil-sand hydrotransporting lines. Due to gravity settling of sand and larger particulates during fluid transport, the majority of the erosion tends to occur along the bottom of the pipeline. To increase the lifetime of individual pipeline sections, the pipeline sections are rotated approximately 90 degrees on a set maintenance schedule, such that a non-eroded internal pipeline surface is positioned at the bottom of a given pipeline section once the pipeline is placed back into service. Once a given pipeline section has been rotated three times, it is typically replaced rather than being rotated again, since all of the internal pipeline surfaces will have experienced potentially eroding conditions after that time.

When high-manganese steels are used to form a pipeline, connecting adjacent pipeline sections together may be problematic in view of the common practice of rotating the individual pipeline sections on a set maintenance schedule. If adjacent pipeline sections are welded together, the weld needs to be broken and subsequently reformed so that the pipeline sections may be rotated. This approach can be very labor intensive and expensive. Another option for joining adjacent pipeline sections together is to employ a flange, such as a weld neck flange. However, the difficulty of machining high-manganese steels into parts having even modestly complex shapes may preclude forming a flange from the same type of steel forming the pipeline section. As an example of present solutions available to address this issue, a readily machined steel composition (e.g., a carbon steel) may need to be used for fabrication of pipeline connectors such as flanges, elbows, T-joints and the like to be used in combination with pipeline sections comprising a high-manganese steel. As such, the pipeline connectors may undergo wear at a different rate than do the pipeline sections comprising the high-manganese steel, and the pipeline sections and the pipeline connectors may be subject to differing maintenance schedules as a result. The differing maintenance schedules can be challenging to manage and may result in further pipeline downtime and increased operational costs.

SUMMARY

In some embodiments, the present disclosure provides hot pressing processes comprising: providing a plurality of particulates comprising a high-manganese steel; loading a container with the plurality of particulates, the container having an internal surface formed in a near-net shape of a part; establishing a reduced pressure state in the container after loading the container with the plurality of particulates, and sealing the container to maintain the reduced pressure state therein, thereby affording a sealed container; placing the sealed container in a pressure vessel; heating the pressure vessel at a predetermined temperature while applying a predetermined pressure isostatically to an exterior surface of the sealed container with a pressurizing gas; wherein the predetermined temperature and the predetermined pressure in combination are sufficient to consolidate the plurality of particulates to form a densified part having the near-net shape; and removing the sealed container to expose a surface of the densified part.

In other embodiments, the present disclosure provides powder consolidation processes comprising: providing a plurality of particulates comprising a high-manganese steel; introducing the plurality of particulates and a binder material into a mold having an internal surface formed in a near-net shape of a part; setting the binder material to form a first intermediate part in which the plurality of particulates remain in a substantially unconsolidated state; removing the first intermediate part from the mold; heating the first intermediate part at a first temperature sufficient to remove the binder material while leaving the plurality of particulates in the substantially unconsolidated state, thereby forming a second intermediate part; and heating the second intermediate part at a second temperature sufficient to consolidate the plurality of particulates together to form a densified part.

DETAILED DESCRIPTION

The present disclosure generally relates to powder metallurgical processes for manipulating high-manganese steels into parts having a desired near-net shape and, more specifically, hot pressing and powder injection molding techniques for processing high-manganese steels.

As discussed above, high-manganese steels may be used in various applications in which good mechanical strength and corrosion and erosion resistance are desirable. Although pipeline sections (line pipe) may be satisfactorily fabricated from high-manganese steels, parts having more complex shapes are often not able to be produced by machining Without being bound by any theory or mechanism, the difficulty in machining even modestly complex parts from high-manganese steels is believed to arise from work hardening. Casting of high-manganese steels is not yet a well-developed technology and may lead to production of parts having an inconsistent, unpredictable and/or undesired microstructure. The difficulty in casting or machining high-manganese steels into parts having even modestly complex shapes significantly limits the range of applications in which these types of steel may be most effectively used. As a non-limiting example, it is presently not believed to be feasible to join together pipeline sections formed from a high-manganese steel using pipeline connectors also formed from a high-manganese steel. As such, the maintenance schedule for the various components of the pipeline may be rather complicated and difficult to manage, thereby leading to increased downtime and operational costs.

The present disclosure provides alternative approaches for manipulating high-manganese steels into parts having a desired shape. In particular, the present disclosure provides powder metallurgical processing techniques for high-manganese steels, such as hot isostatic pressing and powder injection molding techniques, which may afford parts with a desired near-net shape suitable for deployment in various types of applications. In these techniques, powder particulates comprising a high-manganese steel may undergo consolidation into fully densified or near-fully densified parts having a consistent, isotropic microstructure. As a non-limiting example, the present disclosure advantageously allows pipeline connectors, such as weld neck pipe flanges, flanged pipe elbows, and flanged pipe T joints, to be fabricated from high-manganese steels, thereby letting pipeline connectors and pipeline sections to each be formed from a high-manganese steel of identical or similar composition for use in combination with one another. Pipeline connectors formed from a high-manganese steel may provide appreciable economic, operational and maintenance benefits compared to those obtained when significantly different steel compositions are present in a pipeline.

Although hot isostatic pressing and powder injection molding are known techniques for manipulating various types of steel compositions, these techniques are not believed to have been employed previously for processing high-manganese steels. Moreover, hot isostatic pressing and powder injection molding techniques are typically reserved for fabrication of parts having exceedingly complex shapes, unlike parts formed according to the disclosure herein. In particular, pipeline couplings are not exceedingly complex in shape and would ordinarily not be manufactured by a technique such as hot isostatic pressing or powder injection molding, especially when using readily machined or castable steel compositions. In the present case, the difficulty of shaping high-manganese steels by machining makes the foregoing techniques well-suited for fabricating even parts having relatively simple shapes, since they cannot be easily fabricated otherwise. Although it can be particularly advantageous to fabricate pipeline couplings according to the disclosure herein, it is to be appreciated that hot isostatic pressing and powder injection molding techniques may afford similar advantages when used to produce other types of parts formed from high-manganese steels as well.

Before describing the embodiments of the present disclosure in further detail, a listing of terms follows to aid in better understanding the present disclosure.

All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” with respect to the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art. Unless otherwise indicated, room temperature is about 25° C.

As used in the present disclosure and claims, the singular forms “a,” “an,” and “the” include plural forms unless the context clearly dictates otherwise.

The term “and/or” as used in a phrase such as “A and/or B” herein is intended to include “A and B,” “A or B,” “A”, and “B.”

For the purposes of the present disclosure, the new numbering scheme for groups of the Periodic Table is used. In said numbering scheme, the groups (columns) are numbered sequentially from left to right from 1 through 18, excluding the f-block elements (lanthanides and actinides).

The terms “austenite” and “austenitic” refer to a steel metallurgical phase having a face-centered cubic (FCC) atomic crystalline structure.

The terms “martensite” and “martensitic” refer to a steel metallurgical phase that may be formed by diffusionless phase transformation, in which a parent steel (typically austenite) and one or more product phases have a specific orientation relationship.

The term “near-net shape” refers to fabrication of a part in an initial shape that is very close to the final part shape, such that no or minimal machining or surface finishing is needed. Additionally, no or minimal mechanical or metallurgical post-processing steps are needed when obtaining a finalized part.

The term “reduced pressure state” refers to a pressure below atmospheric pressure.

The term “consolidate” refers to the act of adjoining a plurality of discrete particulates into a continuous body having metallurgical bonds between particulates, thereby resulting in a fully integral part.

The terms “densify” and “densification” refer to the removal of at least a portion of voids between a plurality of discrete particulates upon undergoing consolidation to form a continuous body having metallurgical bonds between particulates.

The present disclosure provides techniques for processing powder particulates comprising a high-manganese steel into parts having a desired shape. Illustrative processing techniques that may be suitable for use in the disclosure herein include hot pressing (e.g., hot isostatic pressing) and powder injection molding, each of which is described in more detail herein below. Both techniques may afford a desired part in a near-net shape, which may undergo further particulate consolidation thereafter to provide a fully or near-fully densified part. Parts fabricated according to the disclosure herein may exhibit isotropic properties once formed.

High-manganese steels suitable for use in the disclosure herein have an austenitic microstructure but are otherwise not considered to be particularly limited in composition, provided that powder particulates can be acceptably thrilled from the high-manganese steel and the high-manganese steel has sufficient erosion and corrosion resistance. At a minimum, suitable high-manganese steels comprise iron, carbon and at least about 9 wt. % manganese, along with additional optional alloying elements that may be further present to tailor the properties of the high-manganese steels. Compositional details of illustrative high-manganese steels suitable for use in the disclosure herein are provided herein below.

Iron is the majority element in the high-manganese steels utilized herein. Iron and unavoidable impurities introduced during steel manufacturing account for the balance of elements present in the high-manganese steels once carbon, manganese and additional alloying elements are accounted for.

Typically, sufficient carbon is present in the high-manganese steels discussed herein to aid in stabilizing the austenite phase. Additionally, carbon may serve to strengthen the high-manganese steels through solid solution strengthening, such as through formation of one or more carbides. Excessive carbide formation may reduce toughness, however. For the foregoing reasons, the carbon content in the high-manganese steels may range from about 0.4-0.8 wt. % C, or from about 0.5-0.7 wt. % C, or from about 0.55-0.65 wt. % C.

Manganese is the primary alloying element in high-manganese steels discussed herein. As such, manganese is the second-most prevalent element after iron in the steel compositions. Manganese may particularly aid in stabilizing the austenite phase during cooling and deformation of the steel during processing. Additionally, the amount of manganese may determine how the steels respond or transform when strained. At manganese contents greater than about 25 wt. %, the austenite phase may deform via dislocation slip when it is mechanically strained. At manganese contents ranging from about 15 wt. % to about 25 wt. %, the austenite phase is mildly metastable and may undergo twinning during deformation to result in a high degree of work hardening, very high tensile strength and uniform elongation. At manganese contents less than about 15 wt. %, transformation of the austenite phase into an ϵ-martensite and/or α′-martensite phase may occur upon mechanical straining. For the foregoing reasons, the manganese content in the high-manganese steels may range from about 9-25 wt. % Mn, or about 12-25 wt. % Mn, or about 12-18 wt. % Mn, or about 14-19 wt. % Mn, or about 16-20 wt. % Mn. Manganese contents up to about 30 wt. % or as low as 8 wt. % Mn may also be tolerated in high-manganese steels suitable for use in the present disclosure.

Chromium may be present in the high-manganese steels discussed herein as an optional alloying element due to the ability of this element to facilitate corrosion resistance. The chromium content may be limited based upon one or more of the following considerations: (1) limiting steel costs by avoiding Cr levels that are too high, (2) limiting austenite phase destabilization by Cr levels that are too high, and (3) limiting carbide precipitation for Cr levels that are too high. Typically, the amount of chromium is chosen to convey acceptable corrosion resistance to the high-manganese steels without promoting excessive austenite phase destabilization and/or carbide precipitation. For the foregoing reasons, the chromium content in the high-manganese steels may range from about 4-15 wt. % Cr, or from about 5-10 wt. % Cr, or from about 10-15 wt. % Cr.

Silicon may play one or more of the following roles when included as an optional alloying element: serving as a ferrite stabilizer, promoting ϵ-martensite formation during ambient temperature deformation, and strengthening the austenite phase through solid solution strengthening. The silicon content may be limited to promote sufficient strengthening without inducing excessive ferrite stabilization. For the foregoing reasons, the silicon content in the high-manganese steels may range up to about 3 wt. % Si or up to 1 wt. % Si, including from about 0.01 wt. % Si to about 3 wt. % Si, or from about 0.01 wt. % Si to about 1 wt. % Si, or from about 0.01 wt. % Si to about 0.2 wt. % Si.

Aluminum may serve a ferrite stabilizer when included as an optional alloying element. Significant amounts of aluminum may destabilize the austenite phase during cooling, while lower amounts of aluminum may stabilize the austenite phase to some degree. Stabilization may include action against strain-induced phase transformation during deformation and providing solid solution strengthening. For the foregoing reasons, the aluminum content in the high-manganese steels may range up to about 0.5 wt. % Al or up to about 0.1 wt. % Al, including about 0.001 wt. % Al to about 0.5 wt. % Al, or about 0.001 wt. % Al to about 0.1 wt. % Al, or about 0.001 wt. % Al to about 0.08 wt. % Al.

When included as an optional alloying element, molybdenum may serve as a solid solution strengthener of the austenite phase and may be utilized in small quantities to increase strength. For the foregoing reasons, the molybdenum content in the high-manganese steels may range up to about 5 wt. %, or up to about 1 wt. %, or up to about 0.5 wt. %, or up to about 0.1 wt. %, including from about 0.001 wt. % Mo to about 1 wt. % Mo, or from about 0.001 wt. % Mo to about 0.5 wt. % Mo, or from about 0.001 wt. % Mo to about 0.1 wt. % Mo.

When included as an optional alloying element, nitrogen is an effective solid solution strengthener and a precipitate (nitride) former. In Cr- and Mn-alloyed austenitic steels, the nitrogen solubility limit is typically determined by the equilibrium between the matrix and chromium nitride (e.g., Cr₂N). If the nitrogen content is too high, hot workability (required for manufacturing) may be negatively impacted. For the foregoing reasons, the nitrogen content in the high-manganese steels may range up to about 0.1 wt. % N, or up to about 0.05 wt. % N, or up to about 0.01 wt. % N, or up to 0.008 wt. % N, including about 0.001 wt. % N to about 0.1 wt. % N, or from about 0.001 wt. % N to about 0.05 wt. % N, or from about 0.001 wt. % N to about 0.01 wt. % N, or from about 0.001 wt. % N to about 0.008 wt. % N.

Other alloying elements suitable for inclusion in high-manganese steels may include, but are not limited to, nickel, tungsten, copper, niobium, vanadium, titanium, sulfur, phosphorus, boron, and any combination thereof.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.4-0.8 wt. % C, 12-25 wt. % Mn, 4-15 wt. % Cr, a non-zero amount of Si less than 3 wt. % Si, a non-zero amount of Al less than 0.5 wt. % Al, less than 5 wt. % Mo, a non-zero amount of N less than 0.1 wt. % N, and balance Fe and inevitable impurities. The term “a non-zero amount” refers to a concentration above that of a manufacturing impurity (inevitable impurities) for a particular component in the high-manganese steels discussed herein.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.1-0.4 wt. % C, 15-25 wt. % Mn, 2.0-8.0 wt. % Cr, less than 2.0 wt. % Mo, less than 10 wt. % Ni, less than 0.7 wt. % Si, less than 100 ppm S, less than 200 ppm P, and balance Fe and inevitable impurities. Such high-manganese steels are described in U.S. Patent Application Publication 20170312862, which is incorporated herein by reference in its entirety.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.4-0.8 wt. % C, 18-24 wt. % Mn, less than 6 wt. % Cr, less than 4 wt. % Mo, less than 5 wt. % Ni, 0.4-1.0 wt. % Si, less than 200 ppm S, less than 200 ppm P, and balance Fe and inevitable impurities. Such high-manganese steels are described in U.S. Patent Application Publication 20180021895, which is incorporated herein by reference in its entirety.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.3-1.2 wt. % C, 9-30 wt. % Mn, less than 8 wt. % Cr, less than 6 wt. % Mo, less than 6 wt. % Ni, less than 5 wt. % W, less than 4 wt. % Cu, less than 2 wt. % Nb, less than 2. wt. V, less than 2 wt. % Ti, less than 0.4 wt. % N, less than 1 wt. % B. 0.1-3.0 wt. Si, and at least one of less than 0.3 wt. % S, less than 0.03 wt. % P, and any combination thereof, and balance Fe and inevitable impurities. Such high-manganese steels are described in U.S. Patent Application Publication 20170312861.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.1-1.5 wt. % C, 8-30 wt. % Mn, 11-30 wt. % Cr, and one or more alloying elements selected from Al, Si, Ni, Co, Mo, Nb, Cu, Ti, V, W, N, B, Zr, Hf, and any combination thereof, and balance Fe and inevitable impurities. Such high-manganese steels are described in U.S. Patent Application Publication 20170088910, which is incorporated herein by reference in its entirety.

In any embodiment, suitable high-manganese steels for use in the disclosure herein may comprise: 0.34.2 wt. % C, 9-25 wt. % Mn, 0.5-30 wt. % Cr, and one or more alloying elements selected from Al, Si, Ni, Co, Mo, Nb, Cu, Ti, V, W, N, B, Zr, Hf, and any combination thereof, and balance Fe and inevitable impurities. Such high-manganese steels are described in U.S. Patent Application Publication 20170349983, which is incorporated herein by reference in its entirety.

Methods of the present disclosure may comprise forming a plurality of particulates comprising a chosen high-manganese steel. Suitable techniques for forming particulates of a high-manganese steel may include, for example, gas atomization, details of which will be apparent to one having ordinary skill in the art. in brief, suitable gas atomization techniques may include passing a molten high-manganese steel composition through a nozzle into a jet of inert gas such as nitrogen or argon. Upon contacting the jet of inert gas, atomized droplets of molten high-manganese steel may form, which may subsequently harden into discrete particulates upon cooling. Particulates formed by such techniques may be utilized in either hot pressing or powder injection molding processes described herein.

High-manganese steels may be processed into parts having a desired near-net shape by hot pressing techniques, such as hot isostatic pressing. More particularly, such techniques for processing high-manganese steels into a part may comprise: providing a plurality of particulates comprising a high-manganese steel; loading a container with the plurality of particulates, in which the container has an internal surface formed in a near-net shape of a part; establishing a reduced pressure state in the container after loading the container with the plurality of particulates, and sealing the container to maintain the reduced pressure state therein, thereby affording a sealed container; placing the sealed container in a pressure vessel; heating the pressure vessel at a predetermined temperature while applying a predetermined pressure isostatically to an exterior surface of the sealed container with a pressurizing gas, such that the predetermined temperature and the predetermined pressure in combination are sufficient to consolidate the plurality of particulates to form a densified part having the near-net shape; and removing the sealed container to expose a surface of the densified part.

Materials for forming containers suitable for use in conjunction with the hot pressing techniques disclosed herein may include, for example, any steel composition that is formable and capable of maintaining a vacuum environment. Various carbon steels may be suitable for use in forming the container. The term “can” may be used to describe the “container” housing the plurality of particulates in the hot pressing processes disclosed herein.

Suitable techniques for loading the container with the plurality of particulates are not considered to be particularly limited. Both manual and automated loading approaches are suitable for use in the disclosure herein. In some embodiments, the container may be vibrationally agitated following particulate loading to promote settling of the particulates and to afford more complete filling of the internal space within the container prior to particulate consolidation.

After loading the container with the plurality of particulates, the container may be evacuated by pulling a vacuum thereon and then sealing the container to maintain a reduced pressure state therein. Sealing the container may comprise a seal welding operation, in particular embodiments of the present disclosure. Depending on the material comprising the container, other types of sealing operations may be appropriate as well. Once sealing has taken place, the pressure within the container may range from vacuum pressures up to less than one atmosphere of pressure. Suitable pressure conditions will be familiar to one having ordinary skill in the art.

After sealing the container under a reduced pressure state, the sealed container may then be placed in a pressure vessel (i.e., a pressurizable vessel) capable of being heated to promote consolidation of the particulates without formation of an intermediate liquid phase in the container. The combination of heating at the predetermined temperature and pressurizing at the predetermined pressure is chosen to be effective for consolidating the plurality of particulates into a densified part. In particular embodiments, suitable pressures applied by the pressurizing gas in the pressure vessel may range from about 8 ksi to about 20 ksi. Similarly, suitable temperatures for promoting consolidation of the particulates comprising the high-manganese steel may range from about 700° C. to about 2,000° C.

The pressure within the pressure vessel is applied with a pressurizing gas. The pressurizing gas may comprise an inert gas such as nitrogen or argon, according to particular embodiments of the present disclosure. The pressure applied to the sealed container with the pressurizing gas may be isostatic in character, such that the pressure is applied at substantially the same magnitude in all directions upon the container. It is to be appreciated that the magnitude of the applied pressure may vary at different times throughout the hot isostatic pressing process, provided that the pressure remains isostatically applied.

After particulate consolidation has taken place, processes of the present disclosure may comprise removing the sealed container from the densified part to expose a surface of the densified part. Suitable removal techniques may be dictated by the material comprising the container. Illustrative removal techniques may include, for example, chemical removal or mechanical removal. Mechanical removal may be suitable when the sealed container is not metallurgically bonded to the densified part therein. Mechanical removal may comprise a machining operation, for example, that at least partially disassembles the sealed container to promote its separation from the densified part. Mechanical removal need not necessarily destroy the container in all cases, since slip off separation of the container from the densified part may leave at least a portion of the container suitably intact for reuse in forming additional parts in some instances. Chemical removal may be suitable when the sealed container is metallurgically bonded to an exterior surface of the densified part. Chemical removal of the container may utilize a chemical reaction to promote dissolution or disintegration of the sealed container to promote its separation from the densified part, thereby exposing a surface of the densified part underneath the container.

In particular embodiments, suitable chemical treatments to promote chemical removal of the sealed container may comprise a pickling treatment that dissolves the sealed container or a portion thereof. Pickling treatments for steel compositions will be familiar to one having ordinary skill in the art. In general, when a pickling treatment is to be used for promoting container removal, a proper dwell time may be selected to limit loss of the high-manganese steel once the container has been substantially removed. The container may be fabricated from a carbon steel in any embodiment of the present disclosure.

Grain sizes obtainable in the hot pressing processes of the present disclosure may be fine and equiaxed, which may aid in promoting consistent, isotropic mechanical properties within the part. In contrast, forged or cast components formed from the same high-manganese steel may possess directional properties, either longitudinal or transverse, depending on the particular manufacturing parameters used.

Processing particulates comprising a high-manganese steel into a densified part may also take place by alternative techniques to promote particulate consolidation. In particular embodiments, powder injection molding processes may be used to promote fabrication of densified parts comprising a high-manganese steel.

Powder injection molding processes of the present disclosure may comprise: providing a plurality of particulates comprising a high-manganese steel; introducing the plurality of particulates and a binder material into a mold having an internal surface forming in a near-net shape of a part; setting the binder material to form a first intermediate part within the mold, in which the plurality of particulates remain in a substantially unconsolidated state; removing the first intermediate part from the mold; heating the first intermediate part at a first temperature sufficient to remove the binder material while leaving the plurality of particulates in the substantially unconsolidated state, thereby forming a second intermediate part; and heating the second intermediate part at a second temperature sufficient to consolidate the plurality of particulates together to form a densified part.

Densified parts formed via powder injection molding techniques may be less densified than are those formed through the hot pressing techniques discussed above. Namely, upon removal of the binder material (e.g., by carbonization), voids may remain within the first intermediate part. The voids may not undergo complete filling once the plurality of particulates undergo consolidation to form the second intermediate part. Moreover, part shrinkage may take place when converting the first intermediate part to the second intermediate part due to the presence and filling of the voids. Despite their lower density, densified parts formed via powder injection molding processes may be sufficiently dense for some purposes. In particular, since a phase change does not take place when performing powder injection molding processes, the part shrinkage may be small enough to produce a sufficiently densified part.

In some instances, further densification of parts formed by powder injection molding processes may be desired, in which case the densified part may undergo heating and pressurization in a pressure vessel to promote additional densification of the densified part. Such techniques for further densifying the densified part may resemble the hot pressing techniques discussed above, except for placing the densified part directly in the pressure vessel instead of in a container.

Suitable binder materials for use in powder injection molding processes of the present disclosure are not considered to be particularly limited, provided that the binder material may be suitably dispensed into the mold in conjunction with the plurality of particulates comprising the high-manganese steel. Once hardened, suitable binder materials are also sufficient to hold the plurality of particulates in the near-net shape following removal of the first intermediate part from the mold. Suitable binder materials may be thermally decomposable at the first temperature, so as to promote removal of the binder material and formation of the second intermediate part. In illustrative embodiments, suitable binder materials may include, for example, polymers or waxes. Both thermoplastic and thermosetting polymers may be suitably used. Particularly suitable binder materials may be liquefiable (e.g., by heating) at a temperature below the first temperature, such that the hinder material may be introduced to the mold in a liquid state. Liquid polymer precursors may also be suitably used in this regard. Thereafter, the binder material may undergo setting (e.g., hardening or solidification) to maintain the plurality of particulates and the binder material in a near-net shape defined within the mold.

Powder injection molding processes of the present disclosure may take place with the plurality of particulates mixed with the binder material. That is, according to particular embodiments of the present disclosure, the plurality of particulates and the binder material may be premixed before being introduced to the mold. In other embodiments of the present disclosure, the plurality of particulates and the binder material may be introduced to the mold separately. In more particular embodiments of the present disclosure, the plurality of particulates and the binder material may be separately introduced into the mold. When introduced to the mold separately, the plurality of particulates and the binder material may be disposed heterogeneously within the first intermediate part, according to particular embodiments of the present disclosure.

Moreover, different steel compositions may be disposed heterogeneously within the near-net shape part formed within the mold. For example, in particular embodiments, a first plurality of particulates comprising a high-manganese steel may be disposed in a first location within the near-net shape part, and a second plurality of particulates comprising a different high-manganese steel or a steel composition that is not a high-manganese steel may be disposed at a second location within the near-net shape part. In particular embodiments, the first plurality of particulates comprising the high-manganese steel may be located on or near the surface of the near-net shape part to afford erosion and/or corrosion resistance thereto. In a preferred embodiment, the surface of the near-net shape part to afford erosion and/or corrosion resistance is located at the internal surface of the part, such as the internal wall of a pipe or pipe fitting.

Grain sizes obtainable in the powder injection molding processes of the present disclosure may be fine and equiaxed, which may aid in promoting consistent, isotropic mechanical properties within the part. In contrast, forged or cast components formed from the same high-manganese steel may possess directional properties, either longitudinal or transverse, depending on the particular manufacturing parameters used.

Densified parts formed by the hot pressing and powder injection molding processes disclosed herein are not considered to be particularly limited in form. In particularly advantageous embodiments, however, densified parts formed according to the present disclosure may comprise a pipeline connector. Suitable pipeline connectors that may be formed from a high-manganese steel include, for example, weld neck flanges, flanged elbows, flanged T joints, and similar structures. Design components of these structures will be familiar to one having ordinary skill in the art.

Embodiments Disclosed Herein Include:

A. Hot pressing processes. The processes comprise: providing a plurality of particulates comprising a high-manganese steel; loading a container with the plurality of particulates, the container having an internal surface formed in a near-net shape of a part; establishing a reduced pressure state in the container after loading the container with the plurality of particulates, and sealing the container to maintain the reduced pressure state therein, thereby affording a sealed container; placing the sealed container in a pressure vessel; heating the pressure vessel at a predetermined temperature while applying a predetermined pressure isostatically to an exterior surface of the sealed container with a pressurizing gas; wherein the predetermined temperature and the predetermined pressure in combination are sufficient to consolidate the plurality of particulates to form a densified part having the near-net shape; and removing the sealed container to expose a surface of the densified part.

B. Intermediate part formation processes. The processes comprise: providing a plurality of particulates comprising a high-manganese steel; introducing the plurality of particulates and a binder material into a mold having an internal surface formed in a near-net shape of a part; setting the binder material to form a first intermediate part in which the plurality of particulates remain in a substantially unconsolidated state; removing the first intermediate part from the mold; heating the first intermediate part at a first temperature sufficient to remove the binder material while leaving the plurality of particulates in the substantially unconsolidated state, thereby forming a second intermediate part; and heating the second intermediate part at a second temperature sufficient to consolidate the plurality of particulates together to form a densified part.

Embodiments A and B may have one or more of the following additional elements in any combination:

Element 1: wherein removing the sealed container comprises a pickling treatment that dissolves the container.

Element 2: wherein removing the sealed container comprises a machining operation that disassembles the container.

Element 3: wherein sealing the container comprises a seal welding operation.

Element 4: wherein the densified part is a pipeline connector.

Element 5: wherein the densified part is a weld neck pipe flange.

Element 6: wherein the densified part is a flanged pipe elbow or a flanged pipe T.

Element 7: wherein the predetermined temperature does not lead to formation of a liquid phase in the container.

Element 8: wherein the binder material comprises a polymer or a wax.

Element 9: wherein the further comprises: providing a second plurality of particulates comprising a second high-manganese steel with a different composition from the high-manganese steel or a steel composition that is not a high-manganese steel; wherein the loading the container with the plurality of particulates comprises disposing the plurality of particulates of the high-manganese steel in a first location of the container and disposing plurality of particulates of the second high-manganese steel or the steel composition that is not a high-manganese steel in a second location of the container.

Element 10: wherein the second location of the container is in a location of the container that forms the internal surface of the near-net shape part.

Element 11: wherein introducing the plurality of particulates and the binder material into the mold takes place by injection molding.

Element 12: wherein the plurality of particulates and the binder material are premixed before being introduced to the mold.

Element 13: wherein the plurality of particulates and the binder material are separately introduced into the mold.

Element 14: wherein the plurality of particulates and the binder material are disposed heterogeneously in the first intermediate part.

Element 15: wherein the second temperature does not lead to formation of a liquid phase in the container.

By way of non-limiting example, exemplary combinations applicable to A include, but are not limited to: 1 or 2 and 3; 1 or 2 and 4; 1 or 2 and 5; 1 or 2 and 6; 1 or 2 and 7; 1 or 2, 3 and 4; 1 or 2, 3 and 5; 1 or 2, 3 and 6; 1 or 2, 3 and 7; 3 and 4; 3 and 5; 3 and 6; 3 and 7; 3, 4 and 7; 3, 5 and 7; 3, 6 and 7; 4 and 7; 5 and 7; 6 and 7; and 8 and 9. By way of further non-limiting example, exemplary combinations applicable to B include, but are not limited to: 4 and 8; 5 and 8; 6 and 8; 4 and 11; 5 and 11; 6 and 11; 4 and 12; 5 and 12; 6 and 12; 4 and 13; 5 and 13; 6 and 13; 8 and 11; 8 and 12; 8 and 13; 8, 13 and 14; 8 and 15; 11 and 12; 11 and 13; 11, 13 and 14; 12 and 13; 12-14; 12 and 15; and 13 and 15.

All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

One or more illustrative embodiments are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for one of ordinary skill in the art and having benefit of this disclosure.

Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. 

What is claimed is:
 1. A process comprising: providing a plurality of particulates comprising a high-manganese steel; loading a container with the plurality of particulates, the container having an internal surface formed in a near-net shape of a part; establishing a reduced pressure state in the container after loading the container with the plurality of particulates, and sealing the container to maintain the reduced pressure state therein, thereby affording a sealed container; placing the sealed container in a pressure vessel; heating the pressure vessel at a predetermined temperature while applying a predetermined pressure isostatically to an exterior surface of the sealed container with a pressurizing gas; wherein the predetermined temperature and the predetermined pressure in combination are sufficient to consolidate the plurality of particulates to form a densified part having the near-net shape; and removing the sealed container to expose a surface of the densified part.
 2. The process of claim 1, wherein removing the sealed container comprises a pickling treatment that dissolves the container.
 3. The process of claim 1, wherein removing the sealed container comprises a machining operation that disassembles the container.
 4. The process of claim 1, wherein sealing the container comprises a seal welding operation.
 5. The process of claim 1, wherein the densified part is a pipeline connector.
 6. The process of claim 5, wherein the densified part is a weld neck pipe flange.
 7. The process of claim 5, wherein the densified part is a flanged pipe elbow or a flanged pipe T.
 8. The process of claim 1, wherein the predetermined temperature does not lead to formation of a liquid phase in the container.
 9. The process of claim 1, further comprising: providing a second plurality of particulates comprising a second high-manganese steel with a different composition from the high-manganese steel or a steel composition that is not a high-manganese steel; wherein the loading the container with the plurality of particulates comprises disposing the plurality of particulates of the high-manganese steel in a first location of the container and disposing plurality of particulates of the second high-manganese steel or the steel composition that is not a high-manganese steel in a second location of the container.
 10. The process of claim 9, wherein the second location of the container is in a location of the container that forms the internal surface of the near-net shape part.
 11. A process comprising: providing a plurality of particulates comprising a high-manganese steel; introducing the plurality of particulates and a binder material into a mold having an internal surface formed in a near-net shape of a part; setting the binder material to form a first intermediate part in which the plurality of particulates remain in a substantially unconsolidated state; removing the first intermediate part from the mold; heating the first intermediate part at a first temperature sufficient to remove the binder material while leaving the plurality of particulates in the substantially unconsolidated state, thereby forming a second intermediate part; and heating the second intermediate part at a second temperature sufficient to consolidate the plurality of particulates together to form a densified part.
 12. The process of claim 11, wherein the binder material comprises a polymer or a wax.
 13. The process of claim 11, wherein introducing the plurality of particulates and the binder material into the mold takes place by injection molding.
 14. The process of claim 11, wherein the plurality of particulates and the binder material are premixed before being introduced to the mold.
 15. The process of claim 11, wherein the plurality of particulates and the binder material are separately introduced into the mold.
 16. The process of claim 15, wherein the plurality of particulates and the binder material are disposed heterogeneously in the first intermediate part.
 17. The process of claim 11, wherein the densified part is a pipeline connector.
 18. The process of claim 17, wherein the densified part is a weld neck pipe flange.
 19. The process of claim 17, wherein the densified part is a flanged pipe elbow or a flanged pipe T.
 20. The process of claim 11, wherein the second temperature does not lead to formation of a liquid phase in the container. 